| Heavy metal pollution, owing to the characteristics of permanent, eco-toxicity and biological enrichment, has long been an important subject in the international environmental science fields. Along with the rapid development of economic construction, the increasing amount of sediments arising from dredge and other sources and its consequent disposal has been one of the major environmental promblems in the marine dumping site of Huangmao Island.Based on the monitoring data from the sea areas of Huangmao Island dumping site, the paper conducts a systematic research on the content, distribution and changing rules of heavy metal in seawater, sediments, and marine organisms of this area. In addition, the paper further explores the correlation between the content of heavy metal in sediments and the concentration of heavy metal in seawater, and then deduces out in linear regression a computational formula for calculating the content of some metals in seawater. Besides, the paper also carries out an evaluation concerning potential ecological risks of heavy metal pollutants in sediments of surface layers.The research results and cognitions obtained are listed as follows:(1) During three investigations on heavy metal elements, the only element in seawater that exceeds the quality standard of first class seawater is Pb. The content of Cu also exceeds the standard in some sampling points, while Zn exceeds the standard only in few sites of a single voyage. The content of other 4 types of heavy metal remain on a clean level. As for the horizontal distribution of these elements, the content in northern parts is higher than that of the southern parts in most occasions, presenting a declining trend with H05 as the center, so is the situation on the bottom layer.(2) Surface sediments are slightly contaminated by heavy metals, while Cu is the only element that has exceeded the standard of first class marine segments in some sites. Generally, 7 types of heavy metals are presenting a rising tendency in sediments, among which, Cd is the most remarkable one, with Hg taking the second place. Horizontally, the content of these elements in northern parts is basically higher than that in southern parts, presenting a declining distribution trend, with H05 as the center.(3) Analysis on the principal components of segments shows that, most heavy metals have contributed a lot to the first principal component, while Cr presents a high contribution rate only to the secondary principal component. Related analysis on heavy metals in segments also indicates that, there were good correlations between As and Zn, Cu, Cd, Pb, Hg, between Hg and Zn, Cd, as well as between Cu and Pb, Cd. The coefficient is fixed within the range of 0.686 ~ 0.802, which show this elements except Cr have the similar source of geochemistry and mam-made pollution.(4) The biological quality of crustaceans and fishes in the dumping area is on a normal level, while the only content that exceeded the reference value is As, and there are no other heavy metals that exceed the standard.(5) The correlation between the content of heavy metals in seawater and the content of heavy metals in segments is also inspected. The content of Zn and As in seawater and in seawater is taking on an obvious correlation. Moreover, Cu and Hg in segments are showing a remarkable correlation with seawater of bottom layer. In allusion to the heavy metals with obvious correlations, the formula of relationship between the content of heavy metal in segments and in seawater is deduced out with linear regression.(6) Geological accumulative index, ecological risk index, and comprehensive index are employed in evaluating the potential ecological risks of heavy metals contained in the segments of Huangmao dumping area. According to the evaluation result, the major heavy metal pollutants in the segments of this area are Hg and Cu, taking on a medium and lower pollution degree. |
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